The worst thing an author can do at a book signing (besides sit there like a bump on a log) is not to have a display!
You need to have posters displaying the cover art of your book. You should have a press book or sell sheets so people can read about the book. And you positively need bookmarks to hand to customers!
Get creative with your display. If visiting a store around a holiday, theme your display appropriately. Have a bowl of candy. Have balloons. Set up your display to attract attention!!